By means of soles, shoes are provided with a plethora of properties which can be pronounced in various strengths, depending on the specific type of shoe. Primarily, shoe soles typically have a protective function. They protect the foot of the respective wearer, due to their increased stiffness compared to the shoe shaft, against injuries caused by, e.g., sharp objects on which the wearer may tread. Furthermore, the shoe sole, due to an increased abrasion resistance, usually protects the shoe against excessive wear. In addition, shoe soles can improve the grip of the shoe on the respective ground and thus enable faster movements. A further function of a shoe sole can consist in its providing certain stability. Furthermore, a shoe sole can have a cushioning effect, for example, by absorbing the forces occurring during contact of the shoe with the ground. Finally, a shoe sole can protect the foot from dirt and spray water or provide a plurality of other functionalities.
In order to satisfy this plethora of functionalities, different materials are known from the prior art from which shoe soles can be manufactured. Exemplarily, shoe soles made from ethylene-vinyl-acetate (EVA), thermoplastic polyurethane (TPU), rubber, polypropylene (PP) or polystyrene (PS) are mentioned here. Each of these various materials provides a special combination of different properties which are more or less well-suited for the specific requirements of the respective shoe type. TPU, for example, is very abrasion-resistant and tear-proof. Furthermore, EVA distinguishes itself by a high stability and a relatively good cushioning effect. In addition, the use of expanded materials, in particular of expanded thermoplastic urethane (eTPU), was taken into consideration for the manufacture of a shoe sole. Thus, for example, WO 2005/066250 A1 describes methods for the manufacture of shoes whose shoe shaft is adhesively connected to a sole on the basis of foamed thermoplastic urethane. Expanded thermoplastic urethane distinguishes itself by a low weight and particularly good elasticity and cushioning properties.
In addition to cushioning and absorbing the shock energy produced when the foot treads on the ground, i.e. a cushioning in vertical direction, it is further known form prior art that during running, also shear forces occur in horizontal direction, in particular on grounds where a shoe has a good grip and the shoe is hence stopped abruptly together with the foot when contacting the ground. In case these shear forces cannot be absorbed at least partially by the ground and/or the sole of the shoe, the shear forces are transmitted with undiminished effect to the movement apparatus, in particular the knee. This easily leads to an excessive burdening of the movement apparatus and promotes injuries. On the other hand, excessive shear capacity of the shoe sole would mean a loss of stability, in particular during faster running, which would lead to an increased risk of injuries. The increased shear capacity can also be undesired in specific regions of the sole, since these regions precisely serve to stabilize the foot. Furthermore, an increased shear capacity, e.g. in the area of the toes or of the midfoot, can give the wearer a sensation of slipping of the shoe during running, which can reduce the wear comfort.
In order to solve this problem, sole constructions are known from the prior art, e.g. from DE 102 44 433 B4 and DE 102 44 435 B4, which can absorb in a way that does not strain the joints a part of the shear forces occurring during running. However, a disadvantage of these constructions consists in the fact that such soles are composed of several independent individual parts, have a fairly high weight and are expensive and complex in manufacture.
Moreover, US 2005/0150132 A1 discloses footwear (e.g., shoes, sandals, boots, etc.) that is constructed with small beads stuffed into the footbed, so that the beads can shift about due to pressure on the footbed by the user's foot during normal use. U.S. Pat. No. 7,673,397 B2 discloses an article of footwear with support assembly having a plate and indentations formed therein. U.S. Pat. No. 8,082,684 B2 discloses a sole unit for a shoe having at least one decoupling track between regions of sole unit allowing for the decoupling of the regions in response to forces from foot-ground contact. DE 10 2011 108 744 A1 discloses a method for the manufacture of a sole or part of a sole for a shoe. WO 2007/082838 A1 discloses foams based on thermoplastic polyurethanes. US 2011/0047720 A1 discloses a method of manufacturing a sole assembly for an article of footwear. Finally, WO 2006/015440 A1 discloses a method of forming a composite material.
Starting from the prior art, it is therefore an objective of the present invention to provide better soles for shoes, in particular for sports shoes. A further objective is to provide improved possibilities by means of which the shear capacity of shoe soles can be selectively influenced in specific regions of the sole.